20. Other APIs

In general, any software interrupt interface that passes
parameters in the EAX, EBX, ECX, EDX, ESI, EDI, and EBP
registers will work as long as none of the registers
contains a segment value. In other words, if a software
interrupt interface is completely register based without any
pointers, segment register, or stack parameters, that API
could work under any DPMI implementation.

More complex APIs require the caller to use the translation
services described in section 11.